1. Field of the Invention
The present invention relates to methods for the rapid, sensitive detection of toxic halogenated hydrocarbons based, in part, on use of a modified Fujiwara reaction, and kits for performing the methods.
2. Discussion of the Background
Nearly all municipal water systems throughout the United States disinfect the public water supply through the addition of halogenating agents. However, while these agents kill various microorganisms in the water supply, they unfortunately also result in the production of various halogenated byproducts such as trihalomethanes (THMs).
THMs are a class of four compounds (i.e. chloroform, bromoform, dichlorobromomethane, and dibromochloromethane). These THMs are pathogenic and regulatory limits have been placed on their presence in water. A detection method for THMs must have sensitivity for the four compounds, alone or in combination, at a concentration in the parts per billion, and must demonstrate comparable recognition of the four THM compounds to minimize a bias in the interpretation of samples that may contain individual THMs or mixtures of the compounds.
The literature describes various methods for the measurement of organic halides from aqueous solution. In one method the aqueous solution of organic halide is passed through a packed column of granular activated carbon (GAC). Organic halides are strongly adsorbed and are completely removed from solution. The GAC, with adsorbed organic halide, is burned and total organic halide is determined by mircocoulometric titration. This comprises EPA Methods 9020, Total Organic Halides (TOX).
Organohalogen compounds such as TCE or the THMs, react with pyridine in the presence of base in a process conventionally known as the Fujiwara reaction.
Classical Fujiwara methods were developed for the detection of organohalogens in pyridine, where pyridine was used either as the extraction solvent for biological materials, or as the impinging solvent for air sampling. But classical Fujiwara chemistry, while well documented, has not been thought compatible with the sensitivity and response normalization requirements necessary for use as an effective assay of total THMs (TTHM). The chemistry does not have the prerequisite sensitivity and the sensitivity to each of the four THMs in the population is different. A test method for the determination of TTHM would thus have limited efficacy using the Fujiwara chemistry currently in the literature.
Lugg (Anal. Chem., 1966, 38, 1532) described the optimization of a homogeneous Fujiwara reaction. However, Lugg's method cannot be used to provide an accurate sensitive test for TTHM for the following reasons:
(1) Lugg's reaction is optimized for sensitivity to a single compound such as chloroform. The kinetics of the reaction of chloroform are considerably different than those for the other trihalomethanes, and the proper selection of reaction time is critical to ensuring normalized response. PA1 (2) Lugg uses sodium hydroxide as the base in the Fujiwara reaction. However, the use of metal hydroxides results in turbid reaction mixtures, most likely as a result of formation of insoluble metal halides as a reaction byproduct. Thus, the sample absorbance cannot be measured accurately under such conditions. PA1 a) contacting said aqueous sample with a solid phase extraction medium to essentially quantitatively adsorb trihalomethanes (THMs) from said aqueous sample; PA1 b) eluting the adsorbed THMs from said solid phase extraction medium with pyridine to essentially quantitatively remove THMs from the solid phase extraction medium; PA1 c) contacting the thus formed pyridine solution of eluted THMs with 0.1.+-.0.25% of a base reagent and an amount of water to form a chromophoric product from each THM, wherein said amounts of base and water are sufficient to provide an optical absorption response for each chromophoric product which is approximately equal on a weight/weight basis to an optical absorption response for each of the chromophoric products formed from the other THMs; and PA1 d) determining a concentration of TTHM by measuring an absorption spectrum for the product of step c). PA1 a) contacting said aqueous sample with a solid phase extraction medium, to adsorb said one or more halogenated hydrocarbons, if present, from said aqueous sample; PA1 b) eluting the adsorbed halogenated hydrocarbons from said solid phase extraction medium with an organic solvent capable of essentially quantitative removal of halogenated hydrocarbons from the solid phase extraction medium; PA1 c) contacting, independently, a plurality of aliquots of the eluted halogenated hydrocarbons with pyridine, a base, and from 0-18% by volume of water, wherein each aliquot is contacted with a volume of water different from all other aliquots; PA1 d) determining the presence, identity or concentration, or a combination thereof, of each halogenated hydrocarbon in the aqueous sample based on a set of kinetic absorbance spectra obtained by measuring absorbance of each aliquot at a time, t, after said contacting step c).
Miller et al. U.S. Pat. No. 4,666,672 refers to the fluorometric detection of halogenated hydrocarbons using the Fujiwara reaction in a two phase system (pyridine or nicotinamide with an aqueous hydroxide). In particular, an optrode which detects halogenated hydrocarbons is shown. The difficulties of quantifying the presence of halogenated hydrocarbons by the Fujiwara reaction are discussed.
Anderson, deceased et al, U. S. Pat. No. 4,929,562 pertains to a method and optrode for detecting gem halogenated hydrocarbons based on a single phase Fujiwara reaction which uses a hindered nitrogen base. Pyridine is used in an amount of from 60-96% by volume based on the volume of the aqueous solution which contains the hindered nitrogen base. It is also stated that the absorption bands depend upon the reactants and hydrocarbon present. However, the dependence of the reaction products absorbance on the concentration of water is not addressed.
In order for an assay for total THM to be useful, the response of the assay must be normalized to provide equivalent detection of each member of the THMs on a weight basis. However, the normalization of THM response is difficult to achieve. Reasons for this include that (1) the THMs vary in molecular weight by more than twofold (chloroform=119, bromoform=253), giving twice the number of chloroform molecules on a per weight basis; (2) they vary in halogen type and stoichiometry and (3) the kinetics of formation of the Fujiwara reaction product varies among the compounds, causing differences in the chromogenic response of the Fujiwara reaction product. Thus on a weight basis, any assay reaction product of chloroform would be expected to generate more than twice the signal produced by the same weight of bromoform.